For hybrid vehicles two or more drive units are combined with one another, which in different manners provide the power required for operating the vehicle. Due to the fact that the features of an internal combustion engine and an electric motor complement one another in a particularly beneficial manner, presently common hybrid vehicles are mostly provided with a combination of an internal combustion engine and an electric motor. The operation of the vehicle occurs via the electric motor primarily in the range of small loads, because the internal combustion motors provide considerably lower levels of effectiveness under partial load than under full load. Under higher loads the operation occurs preferably via the internal combustion engine, because then the electric energy accumulator, from which the electric motor is supplied during operation, can be recharged with relatively good effectiveness by an additional generating operation of the electric motor. In order to increase the maximum torque provided for the vehicle, additionally the release of momentum from the internal combustion engine and the electric motor can also occur parallel.
In multi-cylinder internal combustion engines, a higher overall effectiveness can be achieved by switching off some cylinders, because the remaining cylinders can be operated with higher effectiveness. A hybrid drive with a thermal engine is known from DE 100 06 743 A1, for example, which is provided with the possibility to switch off cylinders in order to avoid any operation under partial load.
When some cylinders are switched off, an internal combustion engine usually operates with a higher level of cyclic irregularities than when all cylinders operate, because the ignition intervals are lengthened. An increase of the level of cyclic irregularity can result in loss of comfort and an increased wear of motor and drive components.
Switching off cylinders is preferably used in motors with high numbers of cylinders, for example, 8 or 12 cylinder motors, switching off N/2-cylinders. Here, in motors with high numbers of cylinders a sufficiently high number of cylinders can still be ignited with constant ignition intervals, even when half of the cylinders are switched off, so that an acceptable engine smoothness with respect to comfort can still be achieved. However, in motors with few cylinders only a loss of comfort has to be expected when some cylinders are switched off.
In addition to concepts, in which only the fuel supply to the cylinders switched off is interrupted or the fresh air or air mixture supply is interrupted via throttles, it is known to perform the switching off via a control of the inlet and outlet valves. For example, from DE 102 04 129 a hybrid vehicle is known, in which, for the purpose of a low vibration when the internal combustion engine is switched off, additionally condensing means are released, in particular in a piston. The release of the condensing means can be achieved by opening a throttle, shortening a compression phase, shortening the time, at which both the inlet and the outlet valves are simultaneously closed, a permanent opening of the inlet and outlet valves or the like. Additionally, one or more cylinders of the internal combustion engine can be switched off mechanically. This can be achieved such that a cylinder control addresses the inlet and outlet valve, either directly or indirectly or via a control for the camshaft such, that the outlet and the inlet valve of the combustion chamber are permanently opened or closed when the internal combustion engine is switched off.